The non weightbearing bit will be the worst (unless he's so physical that hoiking his bodyweight around on his arms is no hardship). Odds are that the crutches will rub his forearms and his palms will be bruised - lots of time spent ensuring they are exactly the right height helps (and, with the NHS, that they're actually a matching pair), plus long sleeved tops and cycling gloves to reduce the pressure.
If it's still too much, pipe insulation will help reduce the impact of the handles - or hastily gaffertaped bubblewrap in a pinch. He might agree to a wheelchair just so he can get out if he's really struggling with cabin fever.
As soon as weighbearing happens, it's incredibly freeing in comparison - but for any cast, you need suitable trousers - joggers or wider legged jeans (or cargo shorts in summer). Make sure he wears boxers for cast checks, as if they need to redo it, they might make it thicker and his trousers need to come off in the process don't ask me how I know this one.
Cold packs help with the itches. NO KNITTING NEEDLES.
Get a waterproof cast bag so he doesn't have to worry about getting it wet.
Once he's onto the Robocop boot, odds are he'll abandon the crutches and start doing more than you expected. it's possible to sprint wearing one as long as you don't mind running like the Terminator
Part of doing more is having some rather spectacular spills. Dancing in a pub was a highlight, right up til the moment I wobbled on the boot and took out an entire table of drinks
You'll need lots of loose, warm, stretchy socks and, depending upon how large the casts are, it might be possible to get a larger size trainer on over the top - I went from size 6 and a half to size 9 when I desperately needed to go back to work.
Don't buy so many snacks if he's likely to munch all day. At least at the start, he won't be in much of a position to go round the shops to buy them himself.
Get a rail for getting in and out of the garden.
Get a stool for sitting down in the shower.
Make sure there are completely clear floors everywhere and walkways aren't cluttered by things, loose rugs or stuff that could catch under the crutches/cast or on his arms. Going upstairs on your knees to bed is better for your mindset than mithering away on the sofa.
And as soon as possible, get him outside. Swimming is possible with some of the cast bags, if the pool has a shallow slope or steps (no hoiking himself up and down pool ladders).
And he needs to do exactly as he's told by his Physio. Even when it hurts. Even when they say 'do more', 'wiggle your toes lots', 'get back on the wobble board and play catch' or 'do less'.
Qualification: I just about avoided what was essentially amputating the foot and reattaching it again surgery by doing what I was told sort of, as the dancing and running wasn't in their list of Good Ideas. It's not perfect by any stretch of the imagination, but it still works as a foot, which is enough for me. A friend didn't avoid it and still has pain now, but again, at least she can walk, which she couldn't leading up to the surgery.